Grease compositions having high tractive coefficients

ABSTRACT

GREASES HAVING HIGH COEFFICIENTS OF TRACTION ARE PREPARED BY THICKENING TRACTIVE FLUIDS COMPRISING SYNTHETIC CYCLIC HYDROCARBONS HAVING A COEFFICIENT OF TRACTION IN EXCESS OF ABOUT 0.06 WITH AN ORGANIC OR INORGANIC THICKENER SUCH AS SILICA OR POLYUREA. THE GREASES ARE USEFUL AS LUBRICATING AGENTS AND AS POWER TRANSMITTING FLUIDS IN TRACTIVE DRIVES.

United States Patent US. Cl. 252-28 11 Claims ABSTRACT OF THE DISCLOSURE Greases having high coeflicients of traction are prepared by thickening tractive fluids comprising synthetic cyclic hydrocarbons having a coeflicient of traction in excess of about 0.06 with an organic or inorganic thickener such as silica or polyurea. The greases are useful as lubricating agents and as power transmitting fluids in tractive drives.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to functional fluids particularly adapted for use in tractive drives and more specifically to greases having high coefl'lcients of traction and comprising mixtures of tractive fluids and organic or inorganic thickening agents.

Description of Prior Art Traction is broadly defined as the adhesive friction of a body on a surface on which it moves. A tractive drive is a device in which torque is transmitted from an input element to an output element through nominal point or line contact typically with a rolling action by virtue of the traction between the contacting elements. While tractive elements are commonly spoken of as being in contact, it is generally accepted that a fluid film is present therebetween. Almost all tractive drives require fluids to remove heat, to prevent wear at the contact surfaces and to lubricate bearings and other moving parts associated with the drive. Thus, instead of metal to metal rolling contact there is a film of fluid introduced into the contact zone and interposed between the metal elements. The nature of this fluid determines to a large extent the limits in performance and the capacity of the drive. Most tractive drives are designed to operate with a tractive fluid which preferably has a coefficient of traction above about 0.06, a viscosity in the range of about 420,000 cs. over a temperature range of 100 F. to 0 F. and good thermal and oxidative stabillty. The fluid should also be noncorrosive to common materials of construction and have good load-bearing and low wear-rate properties.

A detailed discussion of tractive drives and fluid properties is given in US. 3,411,369 and US. Pat. 3,440,- 894. These patents define certain classes of fluids characterized by high coeflicients of traction and preferred molecular structures which were found to be superior for tractive drives. The fluids described in these references generally possess the desirable properties enumerated above and are considered to be among the best of any fluids known for conventional tractive drives with respect to general performance. There are, however, certain applications which place a premium on high tractive coefficient and at the same time do not require the fluid to dissipate large quantities of heat. These applications are generally found in small, light duty, precision type drives such as those used to drive table feeds for milling machines, operate and control textile machinery, operate conveyors and positioning equipment, drive precision displacement pumps, actuate switches, valves, and controls, and many other applications where light duty power transmission is required. Although known tractive fluids can 3,335,050 Patent-ed Sept. 10, 1974 ice be used in these applications, such fluids are specifically designed for heavy duty applications and the fluid properties are not optimum for light duty drives where a premium is placed on tractive coefficient.

It is accordingly an object of the present invention to provide tractive compositions having exceptionally high tractive coeflicients. It is a further object of this invention to provide a new class of greases suitable for use as the power transmitting compositions in tractive drive apparatus.

SUMMARY The novel composit ons of the present invention are prepared by thickening tractive fluids having a coefficient of traction of at least about 0.06 with organic or inorganic thickeners to yield a grease having a coeflicient of traction in excess of 0.10 as measured at 100 F. and 200,000 p.S.i. maximum Hertz stress. The tractive fluid is preferably a compound containing from about 12 to carbon atoms, up to 8 of which can be replaced by oxygen, nitrogen, phosphorus, or silicon, and having a structure which includes either a cyclic radical having at least one saturated carbon-containing ring of at least 6 member atoms or an acyclic radical in which there are at least 3 quaternary carbon atoms. The thickeners are preferably colloidal silica or polyurea. The greases comprise a major amount of a tractive fluid and a minor amount, generally in the range of from about 5 to 25 percent by weight of a thickening agent.

DESCRIPTION OF PREFERRED EMBODIMENTS The compositions of the present invention comprise tractive fluids thickened to a grease consistency by the use of organic or inorganic thickeners. Typical tractive fluids useful in the present invention include those described at lengths in US. Pat. 3,411,369 and US. Pat. 3,440,894. These fluids are defined in terms of certain structural units or elements present within their molecules which render the fluids particularly suitable for use in tractive devices.

As defined in US. Pat. 3,440,894, suitable fluids are those organic compounds (1) having from about 12 to about 70 carbon atoms, up

to 8 of which can be replaced by atoms other than carbon atoms and can be selected from such atoms as oxygen, nitrogen, phosphorus and silicon, and

(2) containing (a) at least one saturated carbon atom containing ring having at least 6 member atoms or (b) an acyclic structure in which there are at least 3 quaternary carbon atoms, and

(3) having a coefiicient of traction of at least 0.06.

Tractants encompassed within the above definition are enumerated in US. Pat. 3,440,894 from column 7 line 26 to column 10 line 57, and this disclosure is specifically incorporated herein by reference.

Examples of particularly preferred tractive fluids encompassed within the above definition are cyclododecane, bicyclohexyl, 1,2-tercyclohexyl, dicyclohexylmethane, 2, 3 dicyclohexyl-Z,S-dimethylbutane, 2,4-dicycloheXyl-2- methyl pentane, and mixtures thereof.

.A nonexclusive list of other suitable tractive compositions includes for example isodecylcyclohexane, isopentadecylcyclohexane, cyclododecane, bicyclohexyl, 4-(1- methylethyl) bicyclohexyl, 4,4-bis( l-methylethyl bicyclohexyl, X-isohexyl 4-isopropylbicyclohexyl, x-cyclopentylbicyclohexyl, dicyclohexylmethane, (x-ethylcyclohexyl) cyclohexylmethane, [x-cyclohexyl( l-methylethyl) ]cyclohexylmethane, bis(2,4,6-trimethylcyclohexyl)methane, 1, 1 dicyclohexylethane, 1,1,3 tricyclohexylpropane, trimethylolpropane tricyclohexanecarboxylate, 1,2-tercycl0- hexyl, 1,3 tercyclohexyl, x (1,1 dimethylbutyl) 1,3 tercyclohexyl, x (1,1 dimethylbutyl) 1,2

tercyclohexyl, 1,2-isopropyltercyclohexyl, 1,3-isopropyltercyclohexyl, bis( 1,3 cyclohexyloxy)-cyclohexane, 1,xbis-(methylcyclohexyl)-cyclohexane, dicyclohexyl cyclohexane 1,3-dicarboxylate, x,x'-quatercyclohexyl, 6-ethyl- 2,2,4,4,11,11,13,13 octamethyltetradecane and 2,2,4,4,13, 13,15,15 octamethylhexadecane, tricyclohexylmethane, N-cyclohexylpiperidine, neopentyl glycol dineotridecanoate, bicyclooctyl, bicyclododecyl, cyclohexyl cyclododecane, cycloheptyl cyclohexanecarboxylate, cyclooctyl cyclohexanecarboxylate, cyclododecyl cyclohexanecarboxylate, bis,cis and trans 1,2-cyclohexyl cyciohexanedicarboxylate, 1,1 dicyclohexyl Z-methylpropane, 1,1-dicyclohexyl-2- methylbutane, 1,1 dicyclohexyl-Z,S-dimethylhexane, 1,1- dicyclohexylpentane, 1,2 dicyclohexylpropane, i,2-di(xethylcyclohexyl)propane, 2,2 dicyclohexylpropane, 2,3- dicyclohexyl 2,3 dimethylbutane, 1,3-dicyclohexyl-2- methylbutane, 1,3-dicyclohexylbutane, 1,2,3-tricyclohexylpropane, and cyclopentamethylene dicyclohexylsilane.

Other suitable and useful tractive fluids are those organic compounds defined in U.S. Pat. 3,411,369 which have a coefiicient of traction of at least about 0.06, and which have from 2 to 9 fused, saturated, carboncontaining rings and from about 9 to about 60 carbon atoms, up to 8 of which can be replaced by atoms other than carbon atoms such as oxygen, nitrogen, phosphorus and silicon. A comprehensive disclosure of suitable fused ring compounds is given in U.S. Pat. 3,411,369 from column 7 line 4 to column 9 line 18, which disclosure is specifically incorporated herein by reference.

A nonexclusive list of some particularly preferred compounds encompassed by this reference include for example cis-Decalin, cisand trans-Decalin, 2,3-dimethylDecalin, isopropylDecalin, t-butylDecalin, perhydrofluorene, perhydrophenanthrene, perhydromethylcyclopentadiene (trimer), perhydrofiuoranthene, 1 cyclohexyl-1,3,3-trimethylhydrindane, x-hexylperhydrofiuoranthene, x-cyclohexylperhydrofluoranthene, poly(ethyl 1 methyl)perhydrofluoranthene, x-isopropylperhydrofiuoranthene, perhydrofiuorene x cyclohexyl, perhydrofiuorene-x-isododecyl, 1 cyclohexylDecalin, 2 (cyclohexyl-x-methyl)- bicyclo(2,2,l)heptane, perhydropyrene, ethylperhydrofluorene, perhydroanthracene, bis Z-Decalin, 1,2-dihydrindane, perhydrocyclopentadiene trimer, 1 cyclohexyl- Decalin, 2 cyclohexylDecalin, dimethyl cyclohexylDecalin, and 4,S-methyleneperhydrophenanthrene.

As evident from the above list of tractive compositions, the useful fused ring compounds can be either substituted or unsubstituted, and the substituents can be alkyl or alicyclic hydrocarbons or heterocyclic carbon-containing ring structures. The alkyl substituents can be either straight chain or branched compounds and can contain from 1 to 18 or more carbon atoms.

The thickening agents can be any of a number of materials commonly used to thicken mineral oils to lubricating viscosity, including both organic and inorganic compositions such as metallic soaps, synthetic polymers, organosiloxanes, clays, bentonite, and colloidal silica.

The metallic soaps most commonly employed as thickeners for mineral oils are the fatty acid soaps of lithium, sodium, calcium and aluminum, and to a lesser extent of potassium, magnesium, barium, and lead. The usual fatty acids used to form such gelling agents are those having from 8 to 32 carbon atoms and may be naphthenic acids, rosin acids, abietic acids, petroleum sulphonic acids or seturated, unsaturated or polar-substituted fatty acids. Saturated fatty acids are, for example, capric, lauric, myristic, palmitic and stearic, and the unsaturated fatty acids are, for example, arachidic, behenic, oleic, linoleic, linolenic, cotton seed fatty acids, palm oil fatty acids, soya bean fatty acids, castor oil fatty acids, tallow fatty acids and tall oil fatty acids. The unsaturated fatty acids may be partially or completely hydrogenated and/ or hydroxylated and/or epoxidized or otherwise oxidized. Other fatty acids include those produced by oxidation of petroleum oils, petroleum waxes and naturally occurring waxes such as montan wax.

The soaps may be of any of the known types, such as those made from the oxides or hydroxides of one or several metals from Groups I, II, III, IV and VIII of Mendeleelfs periodic table. A water-soluble soap such as the sodium, potassium or ammonium soap is usually first prepared and the insoluble metal soap of the organic acid is then precipitated by adding a water-soluble salt of the precipitating metal. Sodium, potassium, lithium, calcium, magnesium, barium, strontium, cadmium, zinc, aluminum, lead, cobalt and tin soaps are effectively used to thicken tractive grease compositions of this invention. Examples of preferred soaps for use either alone or in admixture are: sodium stearate, sodium hydroxystearate, sodium oleate, potassium stearate, potassium rosinate, potassium oleate, lithium stearate, lithium hydroxystearate, lithium rincinoleate, calcium stearate, calcium hydroxystearate, barium stearate, barium hydroxystearate, strontium stearate, cadmium oleate, cadmium stearate, cadmium rosinate, zinc steal-ate, aluminum naphthenates, aluminum stearate, aluminum hydrostearate, lead naphthenates, lead stearate, lead hydroxystearate, magnesium stearate, magnesium oleate, magnesium rosinate, magnesium naphthenate, magnesium hydroxystearate, tin stearates, and tin naphthenates. Soaps of amines such as stearyl amine or triethanolamine may also be used either alone or in conjunction with the metal soaps.

Organic thickeners useful in preparing the tractive greases of this invention include, for example, p-polyphenyl, biphenylene diisocy-anates, monophenylenediisocyanates, arylureas, polyarylureas, 1,3,5-triazene compounds including diamino-alkyl-triazene and diaminoaryl triazene, bis(triphenylsilyl) perfluorodicarboxylic acid esters, alkyl silox-anes, and aryl si'loxanes such as phenylsiloxane.

Inorganic thickeners include materials such as clay, colloidal silica, silica aeroge'l, alumina, graphite, mica, talc and diatomaceous earth.

A Widfi latitude in thickener composition is permitted since the selection of thickeners is not critical to the present invention provided the thickener has no adverse effect upon the tractive coefficient. Particularly preferred organic thickeners which give excellent results to the tractive base stock fluids are the polyureas, and a particularly preferred inorganic thickener is finely divided amorphous silica. Each of these agents provides a grease having excellent physical properties and performance characteristics.

Amorphous silica is conventionally prepared by the high temperature vapor phase hydrolysis of silicon tetrachloride. It may also be prepared by the high temperature vapor phase thermal decomposition of silicon compounds such as silicon esters, or by the high temperature vapor phase hydrolysis of silicon compounds such as silicon esters or silanes with super heated steam. Amorphous silica prepared according to any of these methods is extremely fine with particles ranging in size from 0.015 to 0.020 microns, and is a preferred thickener for tractive grease formulations.

The arylurea and polyarylurea thickeners are readily prepared by reacting arylisocyanates and aryl amines according to conventional procedures. Examples of suitable aryl isocyanates which can be used in the preparation of these thickeners include the following:

1,4-diisocyanato benzene,

1,3-diisocyanato benzene,

1,3,5-triisocyanato benzene,

2,4-tolylene diisocyanate,

2,6-tolylene diisocyanate,

3,S-diisocyanato-t-butyl-benzene,

p,p'-diisocyanato biphenyl,

3,3-dimethylbiphenylene-4-4-diisocyanate,

3,3'-dibutyl-biphenylene-4,4'-diisocyanate,

naphthylene diisocyana-te, diphenylmethane- 4,4'-diisocyanate,

3,3'-dimethyldiphenyl-methane-4,4'-diisocyanate, 3,3-di-t-butyldiphenylmethane-5,5'diisocyanate, p-chlorophenyl isocyanate, p-toyly isocyanate, toluene diisocyanate, p-biphenylyl isocyanate (p-xenyl isocyanate, phenyl isocyanate, p-carboxyphenyl isocyanate, a-naphthyl isocyanate, p,p'-diisocyanato-biphenyl, l,4-diisocyanato-benzene, 2,5-dichlorophenyl isocyanate, o-biphenylyl is'ocyanate, (o-xenyl isocyanate), o-chlorophenyl isocyanate, p,p'-diisocyanatodiphenylmethane,

and mixtures thereof. Examples of aryl amines which can be reacted with the aryl isocyanates include p-biphenylamine, benzidine, p-anisidine, o-tolidine, p-arninophenol, p-amino-benzontrile, p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, aniline, p-chloroaniline, pfiuoroaniline, diaminodurene, p-toluidine, o-toluidine, 1,2, 4-benzenetriamine, 2,5-dichloroaniline, p,p'-oxydianiline, p-aminobenzoic acid, p-amino-biphenyl, benzidine, dianisidene, o-tolidine, p-aminophenol, p-amino-benzonitrile, p-phenylene diamine, m-phenylene diamine, o-phenylene diamine, 2,5-dichloroaniline, aniline, p-toluidine, and mixtures thereof.

The tractive grease compositions of this invention are prepared by dispersing a selected thickener in a tractive fluid by suitable mechanical means such as rapid stirring or milling. The tractive fluid generally comprises a major proportion, i.e'. in excess of about 50% by weight, of the grease composition, while the thickener preferably comprises from about 5% to 25% by weight of the grease, although greater amounts of thickener up to about 50% by weight may be used to advantage in some formulations. I

The coeflicient of traction of the finished grease is determined on a rolling disc test machine which comprises two hardened steel rollers which may be loaded difference in velocities of the two roller surfaces, and is essentially independent of load and the mean velocity of the roller surfaces. In a practical variable speed transmission, the rates of sliding that are of significance in the transmission of power usually range from approximately 1 in./sec. up to in./sec. For comparative purposes, therefore, the best criterion of the tractive capacity of a grease is the value of the coeflicient of traction over this range of sliding.

The tractive coefiicients reported herein were obtained at an operating temperature of 100 F. and a Hertz stress of 200,000 p.s.i. The coeflicients of traction reported are the average coefiicients over a range of from 1 to 8 percent slip at sliding speeds of from 1 in./sec. to 50 in./sec. and a mean surface velocity of from 330 ft./min. to 4,640 ft./min.

The following examples illustrate some typical trastive grease compositions and properties. The examples are presented for purposes of illustration only and are not limiting of the invention.

I. TRACTIVE GREASE COMPOSITIONS Grease AA tractive fluid comprising a base stock of 2,4-dicyclohexyl-Z-methyl pentane (hereinafter designated as TF-l) thickened with 16 percent by weight polyurea.

Grease BTF1 thickened with 9 percent by weight of amorphous silica.

Grease C--A tractive fluid comprising a base stock of equal parts' 2,4-dicyclohexyl-Z-methyl pentane and dicylohexyl-1,2-cyclohexane dicarboxylate (hereinafter designated as TF-2) thickened with 17 percent by weight of polyurea.

Grease DTF2 thickened with 9 percent by weight amorphous silica.

Grease MO-1A 300320 SUS 100 F. viscosity mineral oil thickened with 18-20% by weight sodalime.

Grease MO2A 750-770 SUS 100 F. viscosity one against the other and driven at any required speed. 40 mineral 0i] thickened With a Na'ca p- II. TRACTIVE GREASE PHYSICAL PROPERTIES Grease Property A B C D MO-l Penetration hardness) ASTM D-217:

' Unworkd penetration 230 281 220 280 k d enetration: st? StI OkES 282 286 265 290 270 220 10,000 strokes 287 321 250 330 290 240 Dropping point F.; ASTM 566 +400 +400 +400 +400 +365 +390 Oxidation stability, ASTM D942 1 0 1 2 Rolled stability ASTM 13-183 *Excellent.

The grease is introduced between the rollers and the relationships between applied load, roller sur-face speeds, relative sliding speed between the two rollers, and torque transmitted from one roller to the other through the contact between them are a measure of the potential performance of the grease in a variable speed drive. Literature references on this rolling disc machine include M. A. Plint [Proceedings of the Inst. of Mech. Engrs, vol. 180, pp. 225, 313 (196566)]; The Lubrication of Rollers, I by A. W. Crook Phil. Trans. A250, 387 (1958)]; and The Lubrication of Rollers, IV, Measurements of Friction and Effective Viscosity by A. W. Crook [Phil. Trans. A225, 281 (1963)].

The two test rollers are 1% chromium ball bearings steel hardened to -62 to 65 Rockwell C. They have a diameter of 6 inches and are crowned to a radius of 3 inches to give a spherical contact zone, and are carried at the ends of shafts running in heavy duty ball and roller bearings. Roller surface temperature is indicated by thermocouple which bears lightly against the rim of the lower roller.

Above a certain minimum speed the coefficient of traction is a function of the sliding velocity, e.g., the

This data illustrates the typical grease like properties which are obtained by thickening tractive fluid compositions according to conventional techniques for preparing petroleum based grease stocks.

III. TRACTIVE GREASE, COEFFICIENT OF TRACTION Coeflicient of traction sliding velocity, in./sec.

The preceding data demonstrate the exceptionally high tractive coefiicients which characterize the tractive greases of the present invention. In particular, the tractive greases have an average coefficient of traction of greater than about 0.10 as determined at a sliding velocity of 10 in./ sec. under the conditions of the test described above.

The tractive greases of this invention add a new dimension to tractive compositions and provide means for obtaining exceptionally high performance from tractive drives where power transmission is dependent upon the coeflicient of traction of the tractive fluid. The exceptionally high coefficients of traction provided by these greases have not heretofore been known, and are not now available from any other source. Thus, the discovery that such high coefficients of traction could be provided by the compositions of the instant invention represents a significant advance in the state of the art relating to power transmission, and allows greater power to be derived from smaller units than was heretofore possible. In addition, the use of tractive grease eliminates the need for fluid seals thereby simplifying design of the tractive units and reducing construction and maintenance costs.

The grease compositions of the instant invention can contain any of a variety of additives useful in compounding greases such as for example, antioxidants, corrosion inhibitors, V.I. improvers or other viscosity control agents, EP lubricating agents, and the like. Compositions including such additives are accordingly included within the scope of the present invention as defined in the claims attached hereto.

The embodiments in which an exclusive property or privilege is claimed are defined as follows.

1. A grease composition comprising (A) a grease thickening amount of a thickener, and

(B) a major amount of a tractive fluid consisting essentially of a compound containing from about 12 to 70 carbon atoms, said compound having in its structure a radical selected from the group consisting of cyclic radicals having at least one saturated carbon-containing ring of at least 6 atoms and acyclic radicals of at least 3 quaternary carbon atoms, and said tractive fluid having a coeflicient of traction of at least about 0.06.

2. A grease composition comprising (A) a greasethickening amount of a thickener, and

(B) a major amount of a tractive fluid consisting esing of clay, silica, alumina, graphite, mica, talc, and diatomaceous earth.

5. A composition of Claim 3 wherein the thickener is an organic material selected from the group consisting of metallic soaps, synthetic polyureas, and organosiloxanes.

6. A composition of Claim 1 wherein the tractive fluid is selected from the group consisting of dicyclohexyl, alkyldicyclohexyl, tercyclohexyl, alkyltercyclohexyl, quartercyclohexyl, quinquicyclohexyl, 2,3 dicyclohexyh 2,3-dimei-hylbutane, 2,4-dicyclohexyl-2-methyl pentane, and mixtures thereof. v

7. A composition of Claim 6 wherein the grease contains from about 5 to 25 percent of a thickener selected from the group consisting of silica and polyurea.

8. A composition of Claim-2 wherein the tractive fluid is selected from the group consisting of Decalin, alkyl- Decalin, cyclohexylDecalin, alkylcyclohexyDecalin, 1- cyclohexyl1,3,3,-trimethylhydrindane, and mixtures thereof.

9. A composition of Claim 8 wherein the grease con-' tains from about 5 to 25 percent by Weight-of -a thickener selected from the group consisting of silica and polyurea.

10. A composition of Claim 1 wherein the tractive fluid is 2,4-dicyclohexyl-Z-methyl pentane and the thickener is polyurea.

11. A composition of Claim 1 wherein the tractive fluid is 2,4-dicyclohexyl-2-methyl pentane and the thickener is silica.

References Cited UNITED STATES PATENTS 3,514,401 5/ 1970 Armstrong et al. 252-28 3,411,3'69 11/1968 Hammann et al. 74-200 3,440,894 4/ 1969 Hammann et al. 74-200 3,639,237 2/1972 Curtis 25228 3,431,204 3/1969 Grammarid 252-28 3,640,870 2/ 1972 Gemmill et' al. 252-59 3,730,896 5/1973 Scott et al. 252-59 3,785,974 1/1974 Scott 25259 3,712,864 1/ 1973 Loefller et al 25259 3,793,203 2/1974 Driscoll et al 25251.5 A

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R. 

